The present invention relates to a tank display system for a fuel tank of a motor vehicle having a sensor which measures the level of fuel in the tank and a tank display which indicates this level of fuel. The fuel tank includes a main fuel tank, and a supplementary fuel tank from which the fuel can be emptied into the main tank when the main tank is almost empty. This invention furthermore relates to a method of determining the remaining volume in a fuel tank in which this volume is to be determined.
Such tank displays are known. In their case, the supplementary tank is not an independent part, but rather is formed by a region in the bottom of the main tank, in the manner that the tank has two outlets which are arranged at different heights. Each outlet can be connected to a fuel line by a valve which is developed as fuel switch and is operated by hand. When the tank is full, the upper outlet is to be connected to the fuel line. The region of the bottom of the tank can be connected to the fuel line via the lower outlet. This bottom region, which serves the function of a supplementary tank, contains a minimum volume of fuel which is measured to serve as reserve. Frequently, a sensor is arranged within the tank, with a float acting on a potentiometer, as a result of which the display field receives a signal and indicates the level of fuel present in the tank. In addition, when the minimum volume is reached, the driver is given a optical signal, for instance by means of a light on the display field. This optical signal serves to indicate that the fuel is down to the reserve state. The driver can, therefore, by means of the display for the level of the fuel and the light for the reserve state, estimate how much fuel is available to him. In modern motor vehicles, the display, however, is very inaccurate since the tank is made flatter and flatter and more and more angled and thus measurement of the height of filling leads to large inaccuracies. Thus, this estimate is very unsatisfactory even with a large amount of experience on the part of the driver and leads, particularly in the reserve state, to a great uncertainty as to the amount of fuel still available.